Countersunk

Countersunk refers to a feature or process in which a conical seat is prepared so that a screw head sits flush with or below the surrounding surface. A countersunk hole is shaped with a conical bearing surface, and a countersunk screw has a matching conical head. When driven correctly, the top surface remains smooth and uninterrupted, reducing snagging and providing a neat appearance. Countersinking is common in woodworking, metal fabrication, cabinetry, and hardware installation, where a flush surface is required for panels, lids, or trim.

In fastening, a countersunk screw is designed to sit into a conical recess so that the head lies flush with or below the material’s surface. The seating angle of the screw head must match the angle of the hole or recess. The most widely used flat-head screws have a roughly 82-degree included angle, though other head styles may use 90 degrees, 100 degrees, or other angles. The countersink diameter should accommodate the screw head’s outer diameter, and the depth should be sufficient for the head to sit flush without protrusion or excessive inset.

Creating a countersunk feature involves a countersink tool or countersunk drill bit that forms the conical recess. A pilot hole is often drilled first to guide the screw and reduce the risk of splitting, especially in wood. In machining, countersinking can be performed with hand tools, drill presses, or milling equipment, depending on material and precision requirements.

Overall, countersinking is a standard technique for achieving flush fastener heads and smooth surfaces, with the specific angles and dimensions chosen to match the screw design and the material being joined.